Transcript L7 Proteins with animal origin - e

Lecture 7.
Proteins with animal origin:
proteins of milk, meat and eggs.
Milk composition
Deficient in iron and vitamin C
Milk proteins
Total protein content in milk – 2.9 – 3.5%
Two major types of milk protein
 Caseins (80%)
 Whey proteins: (20%)
Whey (milk serum) is the liquid remaining
after milk coagulation and curds removal. It
contains water, lactose and soluble noncasein proteins.
http://ansci.illinois.edu/static/ansc438/Milkcompsynth/milkcomp_pr
otein.html
Milk protein fractions
Milk proteins
Milk proteins separation by
polyacrylamide gel electrophoresis (by
molecular weight).
Caseins (~25-35 kDa) move more
slowly than major whey proteins ßlactoglobulin (18 kDa) and a-lactalbumin
Larger proteins migrate more
(14 kDa).
Others include primarily lactoferrin (~80
kDa) and serum albumin (~66 kDa).
slowly in the gel and remain nearer
the top of the gel. Smaller proteins
migrate more rapidly toward the
bottom of the gel.
Casein: Casein structure
• Casein is a mixture of at least three similar
proteins (α-casein, β-casein, and κ-casein) which
differ primarily in molecular weight and amount of
phosphorus they contain (number of phosphate
groups).
• Casein fractions differ from each other by charge
distribution along the polypeptide chain, the
content of proline and sensitivity to precipitation
Ca 2+.
• All casein proteins except κ-caseins are
phosphoprotein, which has phosphate groups
attached to some of the amino acid side chains
(mainly serine and threonine).
• α-caseins are the major casein proteins. Its
containing 8-10 phosphate groups. It is poorly
soluble in water.
• β- caseins contains about 5 phosphate residues, it
is more hydrophobic than α-caseins and κ-casein.
It is poorly soluble in water.
• Because α-caseins and β-caseins are highly
phosphorylated, they are very sensitive to the
concentration of calcium salts, that is, they will
precipitate with excess Ca2+ ions.
• κ-caseins are glycoproteins. They contain
carbohydrate part which is negatively charged.
Hydrophilic part.
• Do not precipitate in the presence of Ca2+ ions.
• Protect other caseins from precipitation and make
casein more soluble forming casein micelles.
• In milk, κ-casein combine with α-caseins and βcaseins to form micelle.
 The word “micelle” describes structure not a
single compound. Casein micelles consist of
water, protein, and salts. The non-protein
component of the micelles include calcium
(37.5%) and phosphates (50%)
 Due to the large size, micelles are not considered
to be truly soluble in water. They are rather
dispersed in water and remain suspended in the
form of colloidal suspension.
Casein micelle
under electron microscope.
Hydrophilic casein molecules (κ-caseins) that have an affinity for
water form the outer part of the micelle (hairy part).
•Hydrophobic casein molecule (α-caseins and β- caseins) form the
inner core of the micelle sphere.
•In some proposed models α- and k-casein are on the outside.
http://crystal.che.ncsu.edu/pdfs/Coll_Surf_b_casein_Chen.pdf
Micelles aggregation
Casein can be precipitated:
1. HCl
2. Enzymatically (renin)
http://nzic.org.nz/ChemProcesses/dairy/3E.pdf
1. HCl
 The acidity of the medium increases the solubility
of the minerals so that organic Ca-P contained in
the micelles start to dissolve in the aqueous phase.
 Acidification of milk leads to destabilization of the
casein micelles and aggregation due to the
reduction of electrostatic interactions in their isoelectric point (pH 4.6).
http://nzic.org.nz/ChemProcesses/dairy/3E.pdf
2. Renin (chymosin) enzyme :
It is produced by newborn
ruminant animals in the stomach
to curdle the milk they ingest,
allowing a better absorption.
It is widely used in cheese
production.
It cleaves the peptide bond
between Phe 105 and Met 106 in
the kappa-casein chain.
κ-caseins stabilizes the micelles
and after cleavage, the casein
proteins precipitate under the
influence of the calcium ions.
Use of pepsin or microbial
proteinases may lead to
higher degree of
hydrolyses thus producing
small peptides with bitter
taste.
Production of caseinate
1. Production of acid casein (by reduction of pH with HCl)
2. Addition of dilute alkalis
http://nzic.org.nz/ChemProcesses/dairy/3E.pdf
Sodium caseinate: properties
Properties
White to light yellow color, particles and powders,
odorless, tasteless or with slight peculiar fragrance and
taste. Easily soluble in water.
Performance
Very good water solubility, water absorbability, viscosity,
emulsification characteristic, stabilization of emulsion and
foaming capability.
Toxicity
LDs50 400-500g/kg; FAO/WHO (1985) ruled that there is
no limit on acceptable daily intake (ADI). Besides, FDA
also lists it as GRAS (generally recognized as safe),
without toxicity.
Sodium caseinate: Application
E469 food supplement
Sodium caseinate has strong hydrophilicity and thus wider
application than casein. It can be used in meat, aquatic meat products,
ice cream, biscuit, bread, noodles and other grain products.
Caseinates are mainly used as food supplements – they improve
nutrition features, taste and smell, increase the shelf life and enrich
products with organic amino-acids. They are used in Meat, Bakery and
Confectioner Industry
In meat products (sausages), it can be used to make fat distribution
uniform, and enhance the adhesion property of meat. The dosage in
sausage is 0.2%-0.3%. In the fish cake, it can improve the elasticity.
In bread, biscuit and noodles, the dosage is 0.2%-0.5%; in foreign pastry,
doughnut and chocolate, it is 0.59%-5.0% while in cream milk
beverages, it is 0.2%-0.39%.
Whey proteins
The proteins remaining in the supernatant after precipitation
of caseins at pH 4.6.
Good source of sulfur containing amino-acids (cysteine and
methionine): 8 times more as compared to casein. This is
possibly the mode of anticancer activity.
Exceptionally rich in leucine, isoleucine and valine.
Contains more leucine than in casein, egg and soy protein.
Globular proteins with a higher water solubility
than casein.
Low heat stability and, therefore can be thermally
coagulated. Denaturation increases water
retention power.
Native whey proteins have good gelling and
whipping properties.
The major whey proteins: β-lactoglobulin
Most abundant whey protein.
In vitro, after partial digestion by
endopeptidases of pancreas it acts as
antimicrobial agent and also inhibits replication
of rotavirus in dose dependent manner.
It binds mutagenic heterocyclic amines and
exert anti-cancerogenic effect.
The major whey proteins: α-lactalbumin
 Recently, a folding variant named “BAMLET”from bovin αlactalbumin which is lethal to tumor cells has been
discovered. It selectively enters into tumor cells and induces
apoptosis.
 Improve performance of stress-vulnarable individuals by
increasing brain tryptophan and serotonin activities.
 Improve sleep in human suffering from nutritional
disorders.
 Suitable for fortifying infant formulae due to richness in
essential amino acids.
 Clinical trials with α-lactalbumin enriched infant formula
exhibited antimicrobial activity as well.
Choose your milk source: Amino acid composition
Milk proteins have a balanced amino acid; high quality protein
Milk protein digestibility
Caseins are highly digestible in the intestine and are a
high quality source of amino acids.
Most whey proteins are relatively less digestible in the
intestine.
When substantial whey protein is not digested fully in
the intestine, some of the intact protein may stimulate a
localized intestinal microflora or a systemic immune
response. This is sometimes referred to as milk protein
allergy and is most often thought to be caused by ßlactoglobulin (whey protein).
Meat proteins
The content of protein in meat and meat products is 15-22%.
There are three main groups of proteins in muscle:
Myofibrillar proteins - Myosin (55% of muscle
proteins) and actin (25% of muscle proteins)
 Cytoskeletal proteins which are responsible for
contraction–relaxation of the muscle.
 Balanced amino acid composition
 Complete protein food
 Their functional properties are the main determinants for
the quality of meat and meat products.
https://biot409.files.wordpress.com/2014/02/8-food-biochemistry-and-foodprocessing-2nd-ed-gnv64.pdf
Myosin and actin
 Actin exists in two forms - G- and
F-actin.
 G-actin is a monomeric globular
protein. In the presence of Mg Gactin polymerizes to form a double
strand chain called F-actin.
 Muscle contraction is carried out by
reacting of the globular heads of
myosin with actin chains.
 Process requires the breakdown of
one molecule of ATP.
 This process is supported by many
other proteins, but in small
quantities.
http://www.pansportmedical.ro/english/sports_medicine/articles/Muscle_fiber_a_bidirectional_approach.html
Connective Tissue Proteins
Collagen
The basic unit of a collagen
molecule is a triple-helical structure
composed of three polypeptide
chains that are stabilized via
hydrogen bonds.
Individual tropocollagen
monomers, in turn, are cross-linked
to form fibrils via hydrogen and
covalent bonds.
Connective Tissue Proteins
 Collagen does not contain tryptophan, thus its
chemical score is 0. High level of proline and
glycine.
 Incomplete protein
 A raw material for gelatin making
 There are a high number of cross-linkages in the
collagen fibers that increase with age making
meat tougher in older animals.
Sarcoplasmic Proteins
metabolic enzymes and myoglobin
Myoglobin
 Oxygen-binding protein, back up supply of
oxygen, temporarily store oxygen.
 Conjugated protein containing a polypeptide
chain and a non-protein hem molecule
 Myoglobin and more particularly the oxidation
state of Fe 2+/3+ are responsible for meat color.
The role of Nitrates and Nitrites in Cured Meat Products
Compound
Chemical
Molecular weight
Symbol
Nitrate
NO3
62
Nitrite
NO2
46
Potassium and sodium salts of the nitrate and nitrites
are the most extensively used of all food additives.
Sodium nitrite, rather than sodium nitrate, is the most
commonly used for curing (although in some
products, such as country ham, sodium nitrate is used
because of the long aging period)
http://simplyhealthylifemagazine.blogspot.bg/2012/02/nitrates-nitrites-meat-and-meat.html
When sodium nitrite is added with the salt, the meat develops a red,
then pink color, which is associated with cured meats such as ham,
bacon, hot dogs, and bologna.
Nitrite reacts with the meat myoglobin to cause these color changes, first
converting to the unstable nitrosomyoglobin (bright red), then on
heating, to a more stable nitrosohemochrome, a pink pigment.
During curing added nitrate is ultimately reduced to nitrite by
nonpathogenic organisms.
http://ps.oxfordjournals.org/content/48/2/668.full.pdf+html
Proteins in food processing. 2004. Yada R. Y. (Ed.)
Egg proteins
Egg yolk proteins
Egg yolk contains 15-16% protein.
Complex protein mixture which contain glycoproteins,
phosphoglycoproteins, lipoproteins and
phosphoglycolipoproteins.
Egg yolk proteins are much less studied than the
proteins of egg white.
Proteins of Egg White
Egg white (albumen) consist of approximately 40 proteins.
Ovalbumin
The predominant protein in albumen (54% of
albumen).
• Classified as a phosphoglycoprotein since
carbohydrate and phosphate moieties are attached to
the polypeptide.
• MW of about 45,000, and made up of 3 components,
A1, A2, and A3, which differ in phosphorous content.
• Ovalbumin A1 has two phosphate per molecule, A2
has one, and A3 has none.
• Ovalbumin in solution is readily denatured by
exposure to new surfaces (e.g., shaking) and heat.
Ovalbumin
It has high biological value.
There is no deficiency of essential amino acids. It is
one of few pure proteins that can adequately meet
human nutritional requirements for amino acids.
In high purity crystalline form- as a standard in the
investigation of composition, physical properties,
and structure of proteins.
As a protein standard in molecular weight
determination by SDS-PAGE and size exclusion
chromatography.
Ovotransferrin
A major egg white protein (12% of total egg white protein)
• A monomeric glycoprotein consisting a single polypeptide
chain.
• Possess antiviral and antibacterial activities
• Iron binding protein, transport of iron in a soluble form to
target cells (reversible, two iron atoms/molecule, as Fe3+).
• The most heat liable in egg white: forming aggregation by
heating at 60 °C, resulting in milky white gel.
Lysozyme
A small (Mm 14 kDa), relatively stable protein
with a positive charge, pI ≈ 10.4.
About 3.5% of the total protein in the egg white.
It possesses enzymatic activity – hydrolizates
bacterial cell wall polysaccharide thus exhibiting
antimicrobial activity.
Due to its relatively high positive charge
electrostatically interact with negatively charged
proteins - ionic bond formation.
Ovomucin
 Glycoprotein - about 3.5% of total egg protein.
 Negatively charged - pI 4.5-5.
 It has good functional properties - especially
foaming and emulsifying properties.
 Responsible for the gel characteristics of the egg
white. Ovomucin interact by ion bonding with
lysozyme as well as positively charged albumin
and globulins of wheat and this affects foaming
in foods (cakes type).